The present invention relates to the control of rheological properties of polyester-styrene resin compositions and, more particularly, the control of the rheological properties of polyester-styrene resin compositions by the addition of an organoclay thereto and a method for the preparation of such an organoclay.
Polyester-styrene compositions have found wide spread use, particularly as lay-up resins and gel coats, in the fabrication of a wide variety of products. In particular, polyester-styrene compositions are widely used in the fabrication of fiberglass articles such as boats, automobile body parts and accessories. As polyester-styrene compositions exhibit low viscosity and no thixotropy, it is necessary that a suitable rheological modifier be mixed with the polyester-styrene composition in order to increase viscosity and provide a thixotropic composition functional as a lay-up resin or gel.
It is well-known that organically modified smectites may be added to polyester-styrene composition as rheological modifiers, either in the form of a pregel with styrene or by direct addition, to improve viscosity and provide thixotropy. Smectites are clay minerals, including montmorillonite, saponite, beidellite, and hectorite, which are characterized by their swelling properties and high cation-exchange capacities. Bentonite, a rock term in which the main mineral is smectite, is formed as a result of the alteration of volcanic ash. Smectites, and bentonites, whose exchangeable cations are mainly sodium, are respectively known to those skilled in the art as sodium smectite and sodium bentonite, and those whose exchangeable cations are mainly calcium and/or magnesium are respectively known to those skilled in the art as alkaline earth smectites and alkaline earth bentonite. The cation exchange capacities of pure smectites generally range between 75 milliequivalents per 100 grams clay to 110 milliequivalents per 100 grams clay.
One method of preparing organoclays suitable as rheological modifiers for polyester-styrene compositions is disclosed in U.S. Pat. No. 4,240,951. According to this "wet" processing method, quaternary ammonium salts are reacted with a water fractionated smectite to produce quaternary ammonium montmorillonites which are suitable as rheological modifiers for polyester-styrene resins. The quaternary ammonium salts disclosed in U.S. Pat. No. 4,240,951 for treating the water fractionated smectite are dimethyldialkylammonium halide, dimethyldialkylammonium methyl sulfate, dimethylbenzylalkylammonium halide and dimethylbenzylalkylammonium methyl sulfate, wherein the alkyl group contains at least ten carbon atoms.
In the method disclosed in U.S. Pat. No. 4,240,951, the smectite to be treated is first mixed with water to form a low-solids slurry. The slurry is then fractionated, i.e. screened and then centrifuged, to yield a low-solids slurry consisting essentially of montmorillonite particles less than one micron equivalent spherical diameter. It is only this water fractionated montmorillonite portion of the smectite slurry which is reacted with the quaternary ammonium salt to produce the desired organoclay. Additionally, as the product organoclay is produced in a low-sollids slurry form, the product slurry must be filtered and the filter cake dried, typically for 40 hours at 60 C. in a blower oven, to recover the product organoclay.
It is an object of the present invention to provide a "dry" processed organoclay suitable as a rheological modifier for polyester-styrene compositions.
It is a further object of the present invention to provide a "dry" process for producing organoclay rheological modifiers wherein the step of fractionating the crude smectite prior to treatment is avoided and the whole smectite, not just the montmorillonite portion thereof, is utilized.
It is a still further object of the present invention to provide a process for producing organoclays wherein the drying required to recover the product organoclay is minimized.